Among the twenty common genetically encoded amino acids only cysteine undergoes facile redox chemistry, and as a result can participate in a wide variety of enzyme catalyzed oxidation and reduction reactions (Surdhar and Armstrong (1987) J. Phys. Chem., 91:6532-6537; Licht et al. (1996) Science 271:477-481). Consequently, most biological redox processes require cofactors such as flavins, nicotinamides and metal ions. In rare cases, quinones, derived from the post-translational modification of tyrosine and tryptophan side chains, are used as the redox cofactor (Stubbe and Van der Donk (1998) Chem. Rev., 98:705-762). For example, bovine plasma copper amine oxidase uses 3,4,6-trihydroxy-L-phenylalanine (TOPA) in the conversion of primary amines and molecular oxygen to aldehydes and hydrogen peroxide, respectively (Janes et al. (1990) Science 248:981-987). These amino acid derived redox catalysts are generated by both radical-mediated and enzymatic reactions (Rodgers and Dean (2000) Int. J. Biochem. Cell Biol., 32:945-955). Clearly, the ability to genetically encode additional redox active amino acids, rather than generate them by complex post-translational mechanisms, would significantly enhance the ability to both study and engineer electron transfer processes in proteins. This invention fulfills these and other needs, as will be apparent upon review of the following disclosure.